1. Field of the Invention
The present invention relates generally to lenses for LED (light emitting diode) light sources and, more particularly, to a lens for LED light sources which is used in efficient display and illumination optical systems.
2. Description of the Related Art
Recently, in display and illumination optical systems, the needs of light sources which are environmentally-friendly and highly efficient and have long life spans has increased greatly. To achieve the above-mentioned purpose, studies have been conducted to increase the efficiency and brightness of LEDs. Alternative light sources using LEDs have been developed. Such LED light sources are used in display and illumination optical systems. In particular, according to publications of projects, such as environmentally-friendly televisions, studies and developments for LCDs (liquid crystal displays) using the LED light sources have been increasingly promoted. To meet the above-mentioned technical needs, development of more efficient lenses for LED light sources used in displays and illumination devices are required.
The illumination devices or displays using LED light sources use white LEDs or white light to be created by mixing three primary colors (RGB) as light sources. The white LEDs have superior white light realization. However, in the case that the white LEDs are used in displays, because color tone is distinguishable, color reproducibility is deteriorated. Therefore, typically, light sources using RGB are used as light sources for high definition displays.
FIG. 1 is a view showing an example of conventional light sources for displays. In detail, FIG. 1 shows how to create a white light using an arrangement of LEDs in triple primary colors (RGB).
As shown in FIG. 1, in the case of a display using a triple primary color LED light source 10, because white light (W) is created by mixing LED lights (for example, red, green and blue), a distance (D1, or light emitting distance) from the three primary color LED light source 10 to a screen 20 must be a predetermined value or more. Therefore, the display is increased in thickness.
FIG. 2 is a view showing another example of conventional light sources for displays. In particular, FIG. 2 shows the case of using a light guide panel 40.
In the case of FIG. 2, an LED 30 is placed on a side of the light guide panel 40. A path 32 of light emitted from the LED 30 is defined in the light guide panel 40 and the light is repeatedly reflected by a boundary surface of the light guide panel 40. Therefore, a display having superior uniformity and color adjusting ability can be embodied. However, it is difficult to apply the case of FIG. 2 to a large screen display. As well, the case of FIG. 2 is disadvantageous in that light efficiency is reduced.
In an effort to overcome the above-mentioned problems, lenses which allow light emitted from an LED light source to exit the lens in a circumferential direction were disclosed. A representative example of such lenses was proposed in U.S. Pat. No. 6,679,621, in which a side-emitting type LED and a lens having a reflective surface and a refractive surface are provided. The lens disclosed in U.S. Pat. No. 6,679,621 is characterized in that light emitted from the LED exits the lens through a side surface which is the refractive surface. Another example of lenses having the above-mentioned structure is shown in FIG. 3.
A lens 50 of FIG. 3 includes a bottom surface 52, a reflective surface 54, a first refractive surface 56 which is angled with respect to a center axis 60 of the lens 50, and a second refractive surface 58 which extends from the bottom surface 52 to the first refractive surface 56. Part of the light entering the lens 50 from a focal point (F) of the bottom surface 52 is reflected by the reflective surface 54 and exits the lens 50 through the first refractive surface 56. The remainder of the light exits the lens 50 through the second refractive surface 58.
In the lens 50 of FIG. 3, most light exits the lens 50 through the side surface of the lens 50 which comprises the first and second refractive surfaces. As such, the lens 50 of FIG. 3 is characterized in that light from the LED light source is emitted through the side surface. However, because the single reflective surface 54, which is symmetrical around the center axis 60 of the lens 50, is only used to guide light to the side surface of the lens 50, if the lens 50 is applied to a relatively large LED light source to increase in brightness, some light is not emitted through the side surface, but undesirably passes over an upper portion of the lens 50. Therefore, when the lens 50 of FIG. 3 is used in a display, difficulty in providing uniform light exists.